Who first came up with the idea that the earth was a sphere?

Who first came up with the idea that the earth was a sphere? and how
did they come to it? It seems unthinkable. Or maybe it isn't if they'd
assumed it was like the Sun and the Moon.

It's not, it's an oblate spheroid.

Saul Levy


On 31 Mar 2006 16:11:26 -0800, wrote:


Who first came up with the idea that the earth was a sphere? and how
did they come to it? It seems unthinkable. Or maybe it isn't if they'd
assumed it was like the Sun and the Moon.

Pythagoras is often given credit for this - but it is likely it was one of a
group of associated with him.

--

Leo's up - somewhere,
Jeffrey


Beneath South Carolina skies and clouds and clouds and clouds
-------------------------------------------------------------
--------------------- ----------------------
-------------------------------------------------------------
wrote in message
oups.com...

Who first came up with the idea that the earth was a sphere? and how
did they come to it? It seems unthinkable. Or maybe it isn't if they'd
assumed it was like the Sun and the Moon.

On 31 Mar 2006 16:11:26 -0800, wrote:


Who first came up with the idea that the earth was a sphere? and how
did they come to it? It seems unthinkable. Or maybe it isn't if they'd
assumed it was like the Sun and the Moon.

Ancient Greek astronomers thought the Earth was a sphere. Pythagoras
gave metaphysical arguments for a spherical Earth. Aristotle gave
physical arguments for a spherical Earth. Eratosthenes was able to
estimate the circumference of the Earth from physical observations.

Yes indeed "Pythagoras gave metaphysical arguments for a spherical Earth."
but he or his students based their conclusion on the earth's shadow falling
on the moon which could only be reproduced using a sphere not a disk ... and
in turn they deduced the spherical shape of the moon based upon the
curvature of the terminator. So actually, they based their conclusion on
experimentation - limited as it was.

--

Leo's up - somewhere,
Jeffrey


Beneath South Carolina skies and clouds and clouds and clouds
-------------------------------------------------------------
--------------------- ----------------------
-------------------------------------------------------------
"William Hamblen" wrote in message
...
On 31 Mar 2006 16:11:26 -0800, wrote:


Who first came up with the idea that the earth was a sphere? and how
did they come to it? It seems unthinkable. Or maybe it isn't if they'd
assumed it was like the Sun and the Moon.

Ancient Greek astronomers thought the Earth was a sphere. Pythagoras
gave metaphysical arguments for a spherical Earth. Aristotle gave
physical arguments for a spherical Earth. Eratosthenes was able to
estimate the circumference of the Earth from physical observations.

wrote:
Who first came up with the idea that the earth was a sphere? and how
did they come to it? It seems unthinkable. Or maybe it isn't if they'd
assumed it was like the Sun and the Moon.



Goes back to Pythagoras and the contemplations of the shadow of the
Earth cast upon the Moon during a lunar eclipse always being round no
matter what time the eclipse was observed. Only a sphere casts a round
shadow no matter the direction of illumination.

" Eratosthenes was able to
estimate the circumference of the Earth from physical observations. "

He got it within 1% of the correct value too. He used some geometry,
and the fact that in one city the summer Sun at the solstace was right
overhead at noon, and on the same day it was a few degrees off in
another city some known distance north.

astrobob wrote:

" Eratosthenes was able to
estimate the circumference of the Earth from physical observations. "

He got it within 1% of the correct value too.

Well, I don't think we have precise enough conversion factors for
ancient measures (the _stadion_, in this case) to be sure about that,
but there's no doubt he was quite accurate.

He used some geometry,
and the fact that in one city

"City" is probably an exaggeration: Syene, now Aswan, pretty well
right on the Tropic of Cancer.

the summer Sun at the solstace was right
overhead at noon, and on the same day it was a few degrees off in
another city some known distance north.

Alexandria, where Eratosthenes was the Librarian.

--
Odysseus